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modelling and simulation of reaction mechanisms in early growth of STO thin films from ab initio calculations

COMPUTATIONAL MATERIALS SCIENCE 2010年第4期49卷 845-849页

作者： Yang, Chun Yi, Yu Li, Yan Rong Sichuan Normal Univ Computat Visualizat & Virtual Real Key Lab Sichua Chengdu 610068 Peoples R China Univ Elect Sci & Technol China State Key Lab Elect Thin Films & Integrated Devic Chengdu 610054 Peoples R China Sichuan Normal Univ Coll Chem Chengdu 610068 Peoples R China

Understanding microscopic reaction processes and particle states in the early growth of SrTiO(3) (STO) thin films is very important to control the growth and prepare well-structured STO thin films. To this end, we use a generalized gradient approximation within density functional theory (DFT) at the PW91/DNP level to investigate the reaction processes of Sr, Ti, and O, the formation of SrO and TiO(2), and the microscopic reaction mechanism underlying the formation of STO. We calculate the reaction intermediates, transition states (TSs), and activation energy and explore the STO formation mechanisms using highest-occupied and lowest-unoccupied molecular orbital theory. In addition, several possible conformations of STO molecules are comparatively investigated. We find that in steady-state conformations of STO, the geometry eigenvalue is similar to the STO unit cell, which indicates that SrO, TiO(2), and STO are the primary particle states during the early growth of STO thin films. Because it acts as a combining center, TiO(2) is preferentially formed and, subsequently. SrO combines with these centers to form STO, which is stable and somewhat similar to the STO crystal cell. These mechanisms lead to the formation of perovskite-structured STO thin films. (C) 2010 Published by Elsevier B.V.

关键词： Oxides Thin films Surfaces Ab initio calculations computer modelling and simulation

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A molecular dynamics study of the structural change differences between Au_(225) and Au_(369) clusters on MgO surfaces at low temperature

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Chinese Physics B 2012年第3期21卷 195-200页

作者：张林王绍青陈难先 Institute of Materials Physics and Chemistry College of ScienceNortheastern University Shenyang National Laboratory for Materials Science Institute of Metal ResearchChinese Academy of Sciences Physics of Department Tsinghua University

The differences in structural change between Au225 and Au369 clusters with their （111） facets supported on MgO（100） surfaces at 5 K are studied by using molecular-dynamics simulations with the atomic interchange potentials of the Au/MgO interface. The parameters are obtained from the ab initio energies using the Chen-MSbius inversion method. Analyses of the pair distribution functions show that the two Au clusters use different deformation processes to adjust the distances between the interface atoms, owing to the misfit between the atom distances among the clusters and the substrates. The local structural changes are identified by atomic density profiles.

关键词： interfaces nanostructures computer modelling and simulation molecular dynamics

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Optoelectronic properties of passivated and solvated (ZnO)₆ nanocluster - A DFT/TD-DFT study

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MATERIALS CHEMISTRY AND PHYSICS 2016年 181卷 248-258页

作者： Gopalakrishnan, S. Kolandaivel, P. Bharathiar Univ Dept Phys Coimbatore 641046 Tamil Nadu India

Surface and interaction effects of capping ligands (ammonia, methanol, methylamine and pyridine) influence the properties of semiconductor nanoclusters (NCs), which help to achieve the desired applications. The density functional theory (DFT) and time dependent density functional theory (TD-DFT) methods have been used to study the electronic properties of Zinc Oxide (ZnO) nanoclusters. The partial density of states (PDOS), HOMO-LUMO (E-g) gap, electrostatic potential map (ESP) and the optical absorption and emission spectra have been calculated and used for the opto electronic studies. Significant differences were observed in the electronic structure of passivated (ZnO)(6) NC because of the passivation of four different ligands with the NCs. We found that the pyridine (-C5H5N) passivated NC is the most stable, followed by ammonia (-NH3), methylamine (-MeNH2), and methanol (-MeOH). The partial density of states show that the pyridine (-C5H5N) passivated (ZnO)(6) nanoclusters exhibit wider band gap than the other NCs. The study of HOMO-LUMO gap and excitation spectra show that there is a blue shift in the absorption spectra of the NCs. The electrostatic potential map around the passivated NCs are plotted and the results are found that methanol (-MeOH) capped NC has weak electronegativity than that of the other NCs. This is due to electronic and nuclear charges of different arrangement on the surface structure of the passivated (ZnO)(6) NCs. (C) 2016 Published by Elsevier B.V.

关键词： computer modelling and simulation Electronic structure Nano structures and optical properties

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Influence of yttrium on the interface valence electron density of thermal barrier coatings

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MATERIALS CHEMISTRY AND PHYSICS 2007年第2-3期105卷 278-285页

作者： Li, Zhilin Liu, Wei Wu, Yuanqi Beijing Univ Chem Technol Coll Mat Sci & Engn Beijing 100029 Peoples R China Beijing Univ Chem Technol Coll Chem Engn Beijing 100029 Peoples R China

Most of the bonding layers of thermal barrier coatings contain some yttrium to improve the physical consistency of the substrate and the ceramics layer. But the reason of the improvement and the proper yttrium content are not clear. In this paper, the valence electron densities P-hk1 and P-uvw of the two sides and their difference Delta p(min) of the bonding layer/ceramic layer interface of thermal barrier coatings are calculated with the empirical electron theory in solids and molecules at various bonding layer yttrium content. The results show the following. The addition of yttrium has beneficial effect on the decrease of the interface stress because it decreases the The addition of yttrium can also increase the valence electron density P-hk1 or p(uvw) of the interface and so increase the interface cohesion force. The most effective yttrium content is at 0.4 wt% or so. The deductions accord with the actual coating, so the method can be applied to design the composition of the bonding layer of thermal barrier coatings. Furthermore. the calculation and the analysis methods of the interface valence electron densities can also be extended to other crystal coatings or composites with special orientation relationship, no matter the interface is a alloy/alloy one, a ceramics/alloy one or a ceramics/ceramics one. (c) 2007 Elsevier B.V. All fights reserved.

关键词： alloys coatings interfaces computer modelling and simulation

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Massively parallel microscopic particle-in-cell

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computer PHYSICS COMMUNICATIONS 2017年 219卷 269-285页

作者： Bart, G. Peltz, C. Bigaouette, N. Fennel, T. Brabec, T. Varin, C. Univ Ottawa Dept Phys 150 Louis Pasteur Ottawa ON K1N 6N5 Canada Univ Rostock Inst Phys D-18051 Rostock Germany

The microscopic particle-in-cell (MicPIC) method was developed to model classical light matter interaction in strongly-coupled plasma systems. It effectively overcomes the limitations of the particle-in-cell and molecular dynamics techniques by combining them into a single, unified framework to solve for both electromagnetic wave propagation and atomic-scale collision processes in a self-consistent treatment. Its effective time complexity is O(N), where N is the number of model particles, which is ideal for studying the dynamics of large ensembles. In this paper, we show that through massively parallel, distributed computations, current implementations of the MicPIC approach can handle up to 10(11) particles on an IBM Blue Gene/Q computer with 65 536 physical cores. This allows modelling volumes of matter of approximately 1 mu m(3) at solid gold density, opening a wealth of potential applications of MicPIC in nanophotonics, diffractive X-ray imaging, and strong-field science. (C) 2017 Elsevier B.V. All rights reserved.

关键词： Light matter interaction computer modelling and simulation Molecular dynamics calculations Particle-in-cell method

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Energetic investigation of the adsorption process of CH₄, C₂H₆ and N₂ on activated carbon: Numerical and statistical physics treatment

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PHYSICA B-CONDENSED MATTER 2014年第1期433卷 55-61页

作者： Ben Torkia, Yosra BenYahia, Manel Khalfaoui, Mohamed Al-Muhtaseb, Shaheen A. Ben Lamine, Abdelmottaleb Fac Sci Monastir Lab Quantum Phys Monastir 5019 Tunisia Qatar Univ Dept Chem Engn Doha Qatar

The adsorption energy distribution (AED) function of a commercial activated carbon (BDH-activatecl carbon) was investigated. For this purpose, the integral equation is derived by using a purely analytical statistical physics treatment. The description of the heterogeneity of the adsorbent is significantly clarified by defining the parameter N'(m)(E). This parameter represents the energetic density of the spatial density of the effectively occupied sites. To solve the integral equation, a numerical method was used based on an adequate algorithm. The Langmuir model was adopted as a local adsorption isotherm. This model is developed by using the grand canonical ensemble, which allows defining the physico-chemical parameters involved in the adsorption process. The AED function is estimated by a normal Gaussian [unction. This method is applied to the adsorption isotherms of nitrogen, methane and ethane at different temperatures. The development of the AED using a statistical physics treatment provides an explanation of the gas molecules behaviour during the adsorption process and gives new physical interpretations at microscopic levels. (C) 2013 Elsevier By. All rights reserved.

关键词： Interfaces computer modelling and simulation Adsorption Heterostructures

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Electronic and magnetic properties of modified silicene/graphene hybrid: Ab initio study

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MATERIALS CHEMISTRY AND PHYSICS 2016年 183卷 580-587页

作者： Chowdhury, Suman Jana, Debnarayan Univ Calcutta Dept Phys 92 Acharya Prafulla Chandra Rd Kolkata 700009 WB India

Among other two-dimensional (2D) novel materials, graphene and silicene both have drawn intense research interest among the researchers because they possess some unique intriguing properties which can change the scenario of the current electronic industry. In this work we have studied the electronic and the magnetic properties of a new kind of materials which is the hybrid of these two materials. Density functional theory (DFT) has been employed to calculate the relevant electronic and magnetic properties of this hybrid material. The pristine structure is modified by substitutional doping or by creating vacancy (Y-X, where one Y atom (Si or C) has been replaced by one X atom (B, N, Al, P or void)). The calculations have revealed that void systems are unstable while Si-B and Si-N are most stable ones. It has been noticed that some of these doped structures are magnetic in nature having induced mid-gap states in the system. In particular, Si-void structure is unstable yet it possess the highest magnetic moment of the order of 4 mu(B) (mu(B) being the Bohr magneton). The estimated band gaps of modified silicene/graphene hybrid from spin polarized partial density of states (PDOS) vary between 1.43-2.38 eV and 1.58-2.50 eV for spin-up and spin-down channel respectively. The implication of midgap states has been critically analysed in the light of magnetic nature. This study may be useful to build hybrid spintronic devices with controllable gap for spin up and spin down states. (C) 2016 Elsevier B.V. All rights reserved.

关键词： Semiconductors Magnetic properties Electronic structure computer modelling and simulation

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Effect of backbone on the biaxial retardation of polyimide films in uniaxial stretch

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MATERIALS CHEMISTRY AND PHYSICS 2007年第1期103卷 35-40页

作者： King, Jinn-Shing Whang, Wha-Tzong Lee, Wen-Chin Chang, Li-Ming Natl Chiao Tung Univ Dept Mat Sci & Engn Hsinchu 300 Taiwan Ind Technol Res Inst Mat & Chem Res Labs Hsinchu 310 Taiwan

A biaxial-retardation film prepared from the uniaxial-stretched polyimide (PI) film was developed for compensating the viewing angle of liquid-crystal displays. Good uniformity of in-plane bireffingence in well-stretched PI films was observed visually with two crossed polarizers. The prism coupling method was used to measure the n(x), n(y), n(z), and thickness of the stretched PI films. The birefringence variations of n, - n, (difference of refractive indices between x- and y-axes) and n(x) - n(z) during the stretching process were highly affected by PI structure. The polarizability tensors and intrinsic birefringences of the PI repeat units were estimated by Gaussian 98W. It was found that the stretch-induced birefringence is more related to the average polarizability per volume at the low elongation period. (C) 2006 Elsevier B.V. All rights reserved.

关键词： optical materials polyimide computer modelling and simulation birefringence

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Simulating scratch behavior of polymers with mesoscopic molecular dynamics

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MATERIALS CHEMISTRY AND PHYSICS 2013年第1期139卷 118-124页

作者： Hilbig, Travis Brostow, Witold Simoes, Ricardo Univ N Texas LAPOM Dept Mat Sci & Engn Denton TX 76207 USA Univ N Texas Dept Phys Denton TX 76207 USA Univ Minho Inst Polymers & Composites IPC I3N P-4800058 Guimaraes Portugal Polytech Inst Cavado & Ave Sch Technol P-4750810 Barcelos Portugal

Part replacement and repair is needed in structures with moving parts because of scratchability and wear. In spite of some accumulation of experimental evidence, scratch resistance is still not well understood. We have applied molecular dynamics to study scratch resistance of amorphous polymeric materials through computer simulations. As a first approach, a coarse grain model was created for high density polyethylene at the mesoscale. We have also extended the traditional approach and used real units rather than reduced units (to our knowledge, for the first time), which enable an improved quantification of simulation results. The obtained results include analysis of penetration depth, residual depth and recovery percentage related to indenter force and size. Our results show there is a clear effect from these parameters on the tribological properties. We also discuss a "crooked smile" effect on the scratched surface and the reasons for its appearance. (C) 2013 Elsevier B.V. All rights reserved.

关键词： Molecular dynamics Polymers computer modelling and simulation Tribology and wear

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Pd-H and Ni-H phase diagrams using cluster variation method and Monte Carlo simulation

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PHILOSOPHICAL MAGAZINE 2019年第19期99卷 2376-2392页

作者： Bourgeois, Natacha Cenedese, Pierre Crivello, Jean-Claude Joubert, Jean-Marc UPEC CNRS ICMPE 2 Rue Henri Dunant F-94320 Thiais France

This work focuses on interstitial solid solutions of hydrogen in the face-centred cubic (fcc) host lattice of palladium and nickel, using a first-principles based approach. Cluster Variation Method (CVM) and Monte Carlo simulation algorithms were especially designed, allowing a coupled use of both techniques, to study hydrogen-vacancy interactions inside an fcc metallic host lattice. First-principles calculations provided the H-Vac interaction energies by structure inversion method. The phase diagrams and thermodynamic properties were computed using only theoretical inputs. The mechanisms leading to the formation of the miscibility gaps observed for both Pd-H and Ni-H systems and the hydrogen ordering on palladium interstitial lattice were reproduced without any empirical term.

关键词： Metal hydrides computer modelling and simulation miscibility gap

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